The present invention relates to apparatus for monitoring the condition and/or appearance of elongated rod-shaped articles which form part of or constitute the starting material for or are smokers' products. More particularly, the invention relates to improvements in apparatus for monitoring the exterior of a continuous or discontinuous rod-shaped commodity, such as a filter rod, a cigarette rod, a cigarillo rod, a cigar rod or the like.
It is already known to detect the presence of defects or blemishes of a continuous rod (such as a cigarette rod wherein a web of suitable wrapping material surrounds a rod-like filler consisting of natural, substitute and/or reconstituted tobacco) by causing the rod to pass through a ring-shaped housing which contains means for directing light against the exterior of successive increments of the rod. The rod reflects the light and the thus reflected light is evaluated by a suitable circuit. The results of evaluation are indicative of the condition and/or appearance of the corresponding portions or increments of the rod. It is also known to install in the housing a first light conducting device which directs incident light against the exterior of the running rod and a second light conducting device which directs reflected light against a transducer which generates signals denoting the intensity or another characteristic of reflected light. The signals can be indicative of a variety of defects of the rod (hereinafter referred to as cigarette rod). For example, a spot of adhesive will reflect more light than cigarette paper of which the envelope of a cigarette rod normally consists; therefore, the corresponding signal will indicate the presence of a defect which can be categorized as being of the strong light-reflecting type. On the other hand, a hole in the wrapper of a running rod will allow incident light to impinge upon and to be reflected by the relatively dark shreds of tobacco which form the filler of the cigarette rod; consequently, the intensity of reflected light will be lower and the evaluation of the corresponding signal will lead to the conclusion that the tested portion of the cigarette rod is unsatisfactory owing to the presence of a light-absorbing defect. The same holds true for creases, fold lines or smudges at the exterior of the wrapper. Furthermore, optical monitoring means can be utilized for detection of properly or improperly applied imprints in the form of lettering, symbols and/or a combination of these. Such imprints are customary on cigarettes to denote the name of the manufacturer, the brand name of the cigarette and/or the trademark or trademarks of the manufacturer or distributor. Certain imprints are made by resorting to light-absorbing paints or inks, and certain other imprints are made by resorting to bronze powder which reflects a relatively large quantity of incident light. The generation of regularly recurring signals in response to optical monitoring of a rod which is advanced at a given speed will indicate that the light-absorbing or light-reflecting imprints are properly positioned with reference to the planes in which the rod is to be severed to yield discrete cigarettes or analogous rod-shaped articles constituting or forming part of smokers' products. The absence of regularly recurring signals or the total absence of signals is indicative of undue shifting of the loci of application of imprints or of partial or total failure of the imprinting mechanism.